A “cataract” is a clouding of the lens in the eye that affects vision. Most people develop cataracts due to aging. The condition is not uncommon; it is estimated more than half of all Americans will either have a cataract or have had cataract surgery by age 80.
FIG. 1 is a diagram of the human eye, included for background. The major features of the eye 100 comprise the cornea 101, the anterior chamber 102, the iris 103, the lens capsule 104, the lens 105, the vitreous 106, the retina 107, and the sclera 108. The lens capsule 104 has an anterior surface 109 bordering the anterior chamber 102 and a posterior surface 110 bordering the vitreous 106. Most relevant to cataracts, the lens 105 within the lens capsule 104 is comprised of a nucleus 111 and cortex 112.
As shown in FIG. 1, the lens 105 within the eye 100 lies behind the iris 103. In principle, it focuses light onto the retina 107 at the back of the eye 100 where an image is recorded. The lens 105 also adjusts the focus of the eye 100, allowing it to focus on objects both near and far.
The lens 105 contains protein that is precisely arranged to keep the lens 105 clear and allow light to pass through it. As the eye ages, the protein in the lens 105 may clump together to form a “cataract”. Over time, the cataract may grow larger and obscure a larger portion of the lens 105, making it harder for one to see.
Age-related cataracts affect vision in two ways. The clumps of protein forming the cataract may reduce the sharpness of the image reaching the retina 107. The clouding may become severe enough to cause blurred vision. The lens 105 may slowly change to a yellowish/brownish tint. As the lens 105 ages, objects that once appeared clear may gradually appear to have a brownish tint. While the amount of tinting may be small at first, increased tinting over time may make it more difficult to read and perform other routine activities.
Surgery is currently the only real treatment for cataracts. Each year, ophthalmologists in the United States perform over three million cataract surgeries. The vast majority of cataracts are removed using a procedure called extracapsular cataract extraction (ECCE). ECCE traditionally comprises of several steps. Incisions must first be made to the cornea 101 in order to introduce surgical instruments into the anterior chamber 102. Through the incisions in the cornea 101 and the space of the anterior chamber 102, the surgeon may remove the anterior face of the lens capsule 109 in order to access the lens underneath 105. This phase of the surgery, known as capsulorhexis, is often the most difficult procedure in ECCE.
Having gained access to the lens through capsulorhexis, a small amount of fluid may be injected into the exposed lens capsule 104 to improve access and maneuverability of the lens 105. This phase of the surgery is known as hydrodissection to the skilled artisan.
After loosening the lens, it must be extracted. Traditionally, the lens is manually extracted through a large (usually 10-12 mm) incision made in the cornea 101 or sclera 108. Modern ECCE is usually performed using a micro surgical technique called phacoemulsification, whereby the cataract is emulsified with an ultrasonic handpiece and then suctioned out of the eye through incisions in the cornea 101.
A phacoemulsification tool may be an ultrasonic handpiece with a titanium or steel needle. The tip of the needle may vibrate at an ultrasonic frequency to sculpt and emulsify the cataract while a pump aspirates particles through the tip. In some circumstances, a second fine steel instrument called a “chopper” may be used to access the cataract from a side port to help with “chopping” the nucleus 111 into smaller pieces. Once broken into numerous pieces, each piece of the cataract is emulsified and aspirated out of the eye 100 with suction.
As the nucleus 111 often contains the hardest portion of the cataract, emulsification of the nucleus 111 makes it easier to aspirate the particles. In contrast, the softer outer material from the lens cortex 112 may be removed using only aspiration. After removing the lens material from the eye 100, an intraocular lens implant (IOL) may be placed into the remaining lens capsule 104 to complete the procedure.
One variation on phacoemulsification is sculpting and emulsifying the lens 105 using lasers rather than ultrasonic energy. In particular, femtosecond laser-based cataract surgery is rapidly emerging as a potential technology that allows for improved cornea incision formation and fragmentation of the cataract.
Phacoemulsification and laser-based emulsification, however, still have their shortcomings. Phacoemulsification requires the use of tools that propagate ultrasound energy along the length of the tool, from a proximal transducer to a distal tip. The propagation leads to the transmission of ultrasound energy along the tool to other tissues proximal to the eye 100. Ultrasound tools also generate more heat than would be desirable for a procedure in the eye 100. In addition, the mechanical requirements of propagating the ultrasound wave along the length of the tool often make it rigid and difficult to steer around corners or bends.
Laser-based tools have their own drawbacks. Presently, manually controlled lasers require careful, precise movement since they can easily generate unwanted heat in the eye 100. Laser fibers in the tool are also fragile, and thus easily damaged when attempting to navigate tight corners. Both limitations increase surgery time and raise safety concerns.
An alternative to conventional laser systems, femtosecond laser systems have their advantages and drawbacks as well. Femtosecond laser systems may be used to create entry sites through the cornea 101 and sclera 108 into the eye 100, as well as to remove the anterior face of the capsule 104. Femtosecond laser energy may be focused within the lens nucleus 111 itself, and used to “pre-chop” the lens nucleus 111 into a number of pieces that can then be easily removed with aspiration. Femtosecond lasers, however, can only fragment the central portion of the lens 105 because the iris 103 blocks the peripheral portion of the lens 105. Thus, use of another emulsification technology—ultrasound or conventional laser—is still necessary to fracture and remove the peripheral portion of the cataract in lens 105, extending total procedure time. Furthermore, femtosecond laser systems are also expensive and costly to operate and maintain.
As an alternative to a purely laser-based emulsification, certain systems may use the lasers to generate steam bubbles to create shockwaves to break up the cataract material during emulsification.
FIG. 2 is a diagram of a multimode optical fiber 200 with a flat tip at the distal end 201, included for illustration purposes. At the output of the distal end 201, all laser energy originating from laser source 203, and carried through optical fiber 200, is absorbed at the surface of fiber 200. If the laser energy is high enough, the surrounding water may vaporize and form a steam bubble 202. If the laser continues to output energy, the steam bubble 202 may grow into a cylindrical shape. A cylindrically-shaped steam bubble only occurs when the absorption depth in the water is relatively short; light energy with a wavelength near 3 μm can produce a cylindrically shaped steam bubble while light energy near 2 μm does not. The cylindrically-shaped steam bubble 202 produces a mechanical action that can cut or disrupt tissue.
FIG. 3 is a diagram of a multimode optical fiber 300 with a tapered (cone shaped) tip at the distal end 301, included for illustration purposes. At the output of the distal end 301 of optical fiber 300, all the laser energy may be absorbed at the surface of the cone shaped fiber. If the laser energy is high enough, the water vaporizes and forms steam bubble 302. If the laser continues to output energy, then the steam bubble can grow into a spherically-shaped steam bubble. The dynamics of steam bubble generation can be found in “Effect of microsecond pulse length and tip shape on explosive bubble formation of 2.78 μm Er,Cr;YSGG and 2.94 μm Er:YAG laser”, Paper 8221-12, Proceedings of SPIE, Volume 8221 (Monday 23 Jan. 2013).
In both FIGS. 2 and 3, the steam bubbles generated by the optical fibers are collinear with the optical fiber. Being collinear, the orientation of the steam bubbles relative to the optical fibers create problems in certain applications. For example, during capsulorhexis, where the anterior portion of the lens capsule is removed, the orientation of the steam bubble presents a challenge because the tools are oriented at a steep angle to the lens capsule through incisions at the edge of the cornea.
Therefore, it would be beneficial to have a new method, apparatus, and system for using steam bubbles that are not collinear with the neutral axis of the optical fiber.